MWIR polarizing beamsplitter cube and method of making the same

Abstract

A polarizing beamsplitter cube, such as for midwave infrared spectral applications, comprises two ZnSe 45° prisms, an adhesion layer and a thin-film polarization coating layer that are deposited onto the hypotenuse of the first prism, a refractive index liquid layer that provides an interface between the prisms that defeats total internal reflection when the prisms are joined together, and a urethane adhesive that permanently seals and encapsulates the liquid. The adhesion layer consists of 100 Å thorium fluoride and 50 Å chromium layers. The polarization coating (PC) comprises alternating layers of zinc sulfide (ZnS) and germanium (Ge) which are deposited by vapor deposition.

We claim:  
     
       1. A method of fabricating an infrared beamsplitter from first and second prismatic elements, comprising the steps of: 
       applying a polarization coating to the first prismatic element;  
       placing a refractive index liquid layer on one of said polarization coating and said second prismatic element, said refractive index liquid layer having a refractive index range between 1.705 to 1.800 and a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm;  
       placing said second prismatic element over said first prismatic element so that said liquid coating is contained between said polarization coating and said second prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared; and  
       sealing the edges of said assembly to maintain said refractive index liquid layer between said first prismatic element and said second prismatic element.  
     
     
       2. The method of claim  1 , further comprising the step of sliding said first prismatic element over said polarization coating to establish a reduced uniform thickness of said refractive index liquid layer. 
     
     
       3. The method of claim  1 , wherein said step of applying a polarization coating further includes applying an adhesion layer between said first prismatic element and said polarization coating to increase adhesion of the polarization coating to the first prismatic element. 
     
     
       4. The method of claim  1 , wherein said polarization coating comprises alternating layers of zinc sulfide and germanium. 
     
     
       5. The method of claim  1 , wherein said first and second prismatic elements are made of ZnSe. 
     
     
       6. The beamsplitter of claim  1  further comprising adhesion layer between said first prismatic element and said polarization coating for increasing adhesion of said first prismatic element and said polarization coating. 
     
     
       7. The infrared beamsplitter of claim  6 , wherein said adhesion layer comprises chromium and thorium fluoride. 
     
     
       8. A method of fabricating an infrared beamsplitter from first and second prismatic elements, comprising the steps of: 
       applying a polarization coating to the first prismatic element;  
       placing a liquid coating on one of said polarization coating and said second prismatic element, including forming said liquid coating with a refractive index range between 1.705 to 1.800 and with a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm;  
       placing said second prismatic element over said first prismatic element so that said liquid coating is contained between said polarization coating and said second prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared; and  
       sealing the edges of said assembly to maintain said liquid coating between said first prismatic element and said second prismatic element,  
       wherein said step of applying a polarization coating further includes applying an adhesion layer between said second prismatic element and said polarization coating to increase adhesion of the polarization coating to the first prismatic element, and  
       wherein said adhesion layer comprises chromium and thorium fluoride.  
     
     
       9. A method of fabricating an infrared beamsplitter from first and second prismatic elements, comprising the steps of: 
       applying a polarization coating to the first prismatic element;  
       placing a liquid coating on one of said polarization coating and said second prismatic element;  
       placing said second prismatic element over said first prismatic element so that said liquid coating is contained between said polarization coating and said second prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared; and  
       sealing the edges of said assembly to maintain said liquid coating between said first prismatic element and said second prismatic element,  
       wherein said liquid coating is a refractive index liquid having a refractive index range between 1.705 to 1.800 and a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm.  
     
     
       10. The method of claim  9 , wherein said adhesive is a urethane adhesive compatible with said refractive index liquid. 
     
     
       11. A method of fabricating an infrared beamsplitter from first and second prismatic elements, comprising the steps of: 
       applying a polarization coating to the first prismatic element;  
       placing a liquid coating on one of said polarization coating and said second prismatic element;  
       forming said liquid coating with a refractive index range between 1.705 to 1.800 and with a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm;  
       placing said second prismatic element over said first prismatic element so that said liquid coating is contained between said polarization coating and said second prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared; and  
       sealing the edges of said assembly to maintain said liquid coating between said first prismatic element and said second prismatic element,  
       wherein said step of applying a polarization coating further includes applying an adhesion layer between said second prismatic element and said polarization coating to increase adhesion of the polarization coating to the first prismatic element, and  
       wherein said adhesion layer includes chromium and thorium fluoride.  
     
     
       12. An infrared beamsplitter comprising: 
       a first prismatic element having a surface;  
       a polarization coating on said surface of said first prismatic element;  
       a second prismatic element having a surface aligned with said surface of said first prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared;  
       a refractive index liquid layer occupying space between said surface of said first prismatic element and said surface of said second prismatic element said refractive index liquid layer having a refractive index range between 1.705 to 1.800 and a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm; and  
       a seal maintaining said refractive index liquid layer between said first prismatic element and said second prismatic element.  
     
     
       13. The infrared beamsplitter of claim  12 , wherein said polarization coating comprises alternating layers of zinc sulfide and germanium. 
     
     
       14. The infrared beamsplitter of claim  12 , wherein said first and second prismatic elements are made of ZnSe. 
     
     
       15. An infrared beamsplitter comprising: 
       a first prismatic element having a surface;  
       a polarization coating on said surface of said first prismatic element;  
       a second prismatic element having a surface aligned with said surface of said first prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to bean split infrared:,  
       a liquid coating occupying space between said surface of said first prismatic element and said surface of said second prismatic element; and  
       a seal maintaining said liquid coating between said first prismatic element and said second prismatic element,  
       wherein said liquid coating is a refractive index liquid having a refractive index range between 1.705 to 1.800 and a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm.  
     
     
       16. An infrared beamsplitter comprising: 
       a first prismatic element having a surface;  
       a polarization coating on said surface of said first prismatic element;  
       a second prismatic element having a surface aligned with said surface of said first prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared;  
       a liquid coating occupying space between said surface of said first prismatic element and said surface of said second prismatic element said refractive index liquid layer having a refractive index range between 1.705 to 1.800 and a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared, said thickness being less than 600 nm; and  
       a seal maintaining said liquid coating between said first prismatic element and said second prismatic element,  
       wherein said seal is a urethane adhesive seal compatible with said refractive index liquid.  
     
     
       17. An infrared beamsplitter comprising: 
       a first prismatic element having a surface;  
       a polarization coating on said surface of said first prismatic element;  
       a second prismatic element having a surface aligned with said surface of said first prismatic element, wherein said first and second prismatic elements have matching refractive indexes so as to beamsplit infrared;  
       an adhesion layer between said first prismatic element and said polarization coating for increasing adhesion of said first prismatic element and said polarization coating;  
       a liquid coating occupying space between said surface of said first prismatic element and said surface of said second prismatic element said refractive index liquid layer having a refractive index range between 1.705 to 1.800 and a thickness in combination with the flatness of said polarization coating and the viscosity of said refractive index liquid layer so as to beamsplit infrared said thickness being less than 600 nm; and  
       a seal maintaining said liquid coating between said first prismatic element and said second prismatic element.